1. Field of the Invention
The invention relates to a substrate support chuck for supporting a semiconductor wafer within a semiconductor processing system. More particularly, the invention relates to a monopolar electrostatic chuck having one electrode of the chuck contacting the supported wafer.
2. Description of the Background Art
Electrostatic chucks are used for holding a workpiece in various applications ranging from holding a sheet of paper in a computer graphics plotter to holding a semiconductor wafer within a semiconductor processing system. Although electrostatic chucks vary in design, they all are based on the principal of applying voltage to one or more electrodes in the chuck so as to induce opposite polarity charges in the workpiece and electrodes, respectively. The electrostatic attractive force between the opposite charges presses the workpiece against the chuck, thereby retaining the workpiece.
In semiconductor wafer processing equipment, electrostatic chucks are used for clamping wafers to a support pedestal during processing. The support pedestal may form an electrode as well as a heat sink or source. Such support pedestals are used in etching processes as well as chemical vapor deposition (CVD) or physical vapor deposition (PVD) applications.
More specifically, the electrostatic chuck contains a chuck body formed of a layer of dielectric material covering a conductive pedestal base. In a unipolar or monopolar electrostatic chuck, a voltage is applied to the conductive pedestal base relative to some internal chamber ground reference. The wafer is retained by coulomb force between charge accumulated on the underside of the wafer and the voltage applied to the pedestal base. A plasma generated proximate the chuck supplies a conductive path for the wafer to ground.
This form of monopolar electrostatic chuck requires a plasma to be developed within the chamber before the clamping voltage can be applied to the pedestal base. Consequently, there is a chance that the wafer could move from its position upon the chuck body prior to electrostatic clamping becoming effective. Also, in PVD processing, the wafer is typically heated prior to deposition processing, i.e., prior to generation of a plasma. Therefore, monopolar chucks do not find much use in PVD applications because the plasma necessary for chucking is not available until wafer processing is begun. It would be advantageous if a clamping force of a monopolar chuck could be effective prior to the plasma being developed within the process chamber.
Therefore, there is a need in the art for a monopolar electrostatic chuck that clamps !the wafer without the presence of the plasma within the process chamber.